1. Field of the Invention
This invention relates to extrusion of low temperature glass precursors and subsequent formation of high temperature, geometrically complex glass structures from the extruded glass precursor.
2. Technical Background
While common structures made of glass have become inseparable from our daily lives, the unique properties of glass also allow its use in complex structures for high-technology specialty applications. Photonic crystal fibers, photocatalytic substrates and filtration devices made of glass, for example, belong in the latter category. Such structures are generally geometrically complex, and therefore, are difficult to manufacture. Aside from being geometrically complex, it is desired that these structures possess certain characteristics, such as high UV transparency, high softening temperatures and low thermal expansion, for commercial applications.
Conventional processes for manufacturing such structures include extrusion, among other processes. However, extrusion of conventional glasses to form geometrically complex structures provides many challenges. For example, the softening temperature of conventional glasses used to manufacture complex glass structures (e.g., hard glasses, such as fused silica and fused quartz) can be in the range of around 1550° C.-1700° C. Once softened and melted, extrusion of conventional hard glass would occur at around 1800° C.-2000° C. Accomplishing and extruding glass at these high temperatures is extremely difficult.
As an alternative to high temperature hard glasses, use of low temperature soft glasses in the manufacture of geometrically complex structures is generally known. Such low temperature glasses generally have a softening temperature at around 500° C.-800° C. and are extruded at about 800° C.-1200° C. While low temperature glasses are generally easier to melt and extrude than high temperature glasses, low temperature glasses similarly have issues. Particularly, low temperature glasses often include components other than silica, such as lead, alkali or alkaline earth metals. While incorporation of these other components decreases the softening temperature and allows these glasses to be more effectively extruded, the resulting structures have low UV transparency, low softening temperatures and high thermal expansion, which makes them less desired for commercial applications.
Accordingly, there is a need for glass materials that facilitate effective manufacture of geometrically complex structures, but include the characteristics of high UV transparency, high softening temperatures and low thermal expansion.